Volatile organic lanthanide compounds and methods for the preparation of lanthanide-containing layered materials form these compounds

ABSTRACT

An adduct of a lanthanide (yttrium) β-diketonate and a donor ligand (N-oxide), the adduct being suitable for use in a metal-containing material deposition process, wherein the ligand has Lewis base characteristics that match the Lewis acid characteristics of the lanthanide β-diketonate in the absence of the ligand is described.

The present invention relates to volatile organic lanthanide compounds(adduct complexes) and methods for the preparation oflanthanide-containing layered materials from those compounds.

In particular, the present invention relates to volatile organic yttriumcompounds. In this specification, the term lanthanide includes yttriumas well as all the elements (metals) with atomic numbers 57-71.Lanthanide elements 57-71 in particular are used in opto-electronicmaterials.

BACKGROUND OF THE INVENTION

Lanthanide compounds, especially lanthanide beta-diketonate complexesare of particular interest as starting materials (precursors) forso-called metal-organic chemical vapour deposition (MOCVD) of lanthanide(e.g. yttrium)-containing materials. Important examples are thedeposition of mixed metal oxides which are superconducting at relativelyhigh temperatures, of buffer layers, of anode- and electrolyte materialsfor fuel cells and of magnetic oxides.

Under some circumstances deposition of pure metal may he possible andthe term metal-containing materials as used herein is to be interpretedaccordingly. More than one metal may be present in the metal-containingmaterial (normally metal oxide).

P. Lu, J. Zhao, C. S. Chern, Y. Q. Li, G. A. Kulesha, B. Gallois, P.Norris, B. Kear and F. Cosandey for instance, in J. Mater. Res., 7(1992) 1993, describe the use of the2,2,6,6-tetramethyl-3,5-heptanedione (TMHD) complex of Y, that isY(TMHD)₃, as a precursor for yttrium during MOCVD of 90° K.superconducting YBa₂ Cu₃ O_(7-x). However, in J. Phys., 50:C5 (1989) 981(L. G. Hubert-Pfalzgraf, M. C. Massiani, R. Papiernik and O. Poncelet)and in Appl. Organomet. Chem., 6 (1992) 627 (L. G. Hubert-Pfalzgraf)there is described how water, always present in precursors, and also inthis (commercially available) compound, can lead to hydrolysis duringevaporation in a MOCVD process, with the consequence that the masstransport is not constant during the whole process. In addition,Y(TMHD)₃ has a rather high melting point (170° C.), which means that itis evaporated from the solid phase. Due to the appearance of differencesin crystal shape and crystal size, varying evaporation rates can occur.

Also other volatile, though fluorine-containing, yttrium-β-diketonatesare used, such asyttrium-6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3.5-octanedionatemonohydrate--Y(FOD)₃.H₂ O--, for example in J. Mater. Res., 5 (1990)2706 (D. J. Larkin, L. V. Interrante and A. Bose). This compound alsocontains water and, moreover, gives problems in the deposition of layersand their properties due to the presence of fluorine.

In J. Phys., 50:C5 (1989) 981 (L. G. Hubert-Pfalzgraf, M. C. Massiani,R. Papiernik and O. Poncelet), the easy formation of a coordinationcomplex between an Y(β-diketonate)₃ and for instance dimethylformamide,pyridine or dimethylsulphoxide, is suggested, but no actual exampleswith Y(TMHD)₃ are given. The existence of a number of Ln(TMHD)₃.DMF (Lnis a lanthanide metal) adducts is reported in Inorg. Synth., 11 (1968)94 (K. J. Eisentraut and R. E. Sievers) and in Inorg. Chem., 6 (1967)1933 (J. E. Schwarberg, D. R. Gere, R. E. Sievers and K. J. Eisentraut),but the compound Y(TMHD)₃.DMF is not described.

WO 89/07666 (T. J. Marks and K. H. Dahmen) describes three Y precursors.The first is Y(TMHD)₃ but this is non ideal as it has a high meltingpoint (175°-6° C.) and is mildly moisture sensitive. The second isY(FOD)₃ (FOD=C₃ F₇ COCHCOC(CH₃)₃) but this has a high melting point andalso contains fluorine. The third is Y(ACAC)₃ (ACAC=H₃ CCOCHCOCH₃) andthis has insufficient thermal stability to be an acceptable precursor;it is also high melting (138°-140° C.).

CA 99: 30325w describes adduct complexes ML₃ Q (whereQ=o-phenanthroline, bipyridyl and Ph₃ P=O) but these are so labile thatthey fully disintegrate in the process of mass spectra acquisition.These complexes are not stable materials that can be volatilised intactunder MOCVD conditions.

CA 105: 202067z discloses M(ACAC)₃.nH₂ O and M(ACAC)₃.phen. Apparently,the phenanthroline adduct is more thermally stable than the water adductand is claimed to be sublimed quantitatively under high vacuum. Undermass spectroscopy conditions the phenanthroline adduct decomposes andloses volatile M(ACAC)₃, i.e. is indistinguishable from Y(ACAC)₃, and itis therefore not an ideal MOCVD precursor.

CA 119:194408h (S. R. Drake et al Inorg Chem 1993, 32, 4464) discosesthe dimer {Y(TMHD)₃ }₂.triglyme!. This complex is intrinsically lessvolatile and requires high vacuum in order to sublime intact.

N. Ahmad et al Inorg Chem 1982, 21, 80 say that many adduct complexes ofLn(FOD)₃.nL can be formed. The authors comment on the tendency of theadducts to dissociate. These complexes would therefore be unsuitable forprocesses such as MOCVD.

CA 119: 240398e (S. R. Drake et al, J Chem Soc Dalton Trans 1993, 2379)suggests a tridentate donor could be bound to La (ionic radius1.15--versus Y 0.93). However, this complex would be unsuitable forMOCVD processes and the like as it is involatile and decomposes onattempted sublimation at 175°-195° C. to yield La(TMHD)₃ !.

CA: 151111p discloses the existence of some tris FOD chelates with1-methylpiperazine as a Lewis base donor ligand. The properties of thecomplexes are not discussed.

CA 109: 182505t shows that for adduct complexes Y(ACAC)₃.L (where L=(Me₂N)₃ P=O or Ph₃ P=O), heating M(ACAC)₃.L is accompanied by the transitioninto the gas phase of M(ACAC)₃.L and the decomposition products M(ACAC)₃and L, i.e. these adduct complexes do not volatilise intact.

CA 101: 180535p describes the fragmentation of Ln(ACAC)₃.L andLn(TMHD)₃.L, which involves loss of neutral ligand, during massspectroscopy. It is yet further evidence that adduct complexes withL=phenanthroline, bipyridyl and Ph₃ P=O do not have the desiredproperties for MOCVD processes.

CA 102: 16524j shows that Ln(ACAC)₃.nL where L=acetylacetoneimine,dissociate on attempted sublimation, leaving parent Ln(ACAC)₃ forLn=Dy-Lu, Y. Likewise, these adduct complexes are unsuitable for MOCVDprocesses.

The present invention therefore seeks to overcome the problems ofdissociation and hydrolysis of lanthanide β-diketonates or their Lewisbase adducts during MOCVD processes.

According to a first aspect of the present invention there is providedan adduct of a lanthanide β-diketonate and a donor ligand, the adductbeing suitable for use in a metal-containing material deposition process(preferably a MOCVD process) wherein the donor ligand has Lewis basecharacteristics that match the Lewis acid characteristics of thelanthanide β-diketonate in the absence of the donor ligand (i.e. withoutthe donor ligand). Alternatively this product may be defined as alanthanide β-diketonate complex with a complexing ligand.

According to a second aspect of the present invention there. is provideda metal-containing material deposition process/method (preferably aMOCVD process) comprising the use of an adduct of a lanthanideβ-diketonate and a donor ligand wherein the donor ligand has Lewis basecharacteristics that match the Lewis acid characteristics of thelanthanide β-diketonate in the absence of the donor ligand.

According to a third aspect of the present invention there is providedthe use of an adduct of a lanthanide β-diketonate and a donor ligand ina metal-containing material deposition process (preferably a MOCVDprocess) wherein the donor ligand has Lewis base characteristics thatmatch the Lewis acid characteristics of the lanthanide β-diketonate inthe absence of the donor ligand.

One or more ligands may be present.

Preferably the lanthanide (β-diketonate)-ligand adduct has a meltingpoint of less than about 150° C., more preferably of less than about125° C., even more preferably of less than about 100° C.

Preferably the adduct forming ligand is a neutral donor ligand.

Preferably the ligand is an oxide.

Preferably the oxide is an N-oxide.

Preferably the N-oxide is a pyridine N-oxide.

Preferably the lanthanide is yttrium.

Preferably the metal-containing material deposition process is a MOCVDprocess.

The donor ligand in the lanthanide β-diketonate adducts of the presentinvention has Lewis base characteristics that match the Lewis acidcharacteristics of the lanthanide β-diketonate in the absence of theligand--as according to Pearson hard-soft acid-base theory (J. Am. Chem.Soc. 1963, 85, 3533).

Therefore, if the lanthanide β-diketonate without the donor ligand has ahigh charge density so does the donor ligand. Likewise, if thelanthanide β-diketonate without ligand has a low charge density so doesthe donor ligand.

SUMMARY OF THE INVENTION

The present invention is therefore based on the surprising finding thatif the Lewis base characteristics of an adduct forming ligand match theLewis acid characteristics of the lanthanide β-diketonate without theligand then the resultant lanthanide (β-diketonate)--ligand adducts areparticularly suited for use in metal deposition processes, in particularMOCVD processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a plot of vapor pressure as a function of temperaturefor compounds of the invention and a comparative compound.

FIG. 2 represents the general structure of the lanthanide adducts of theinvention.

DETAILED DESCRIPTION

A key advantage of some of the lanthanide (β-diketonate)--ligand adductcomplexes of the present invention is that they have a low melting point(e.g. less than about 150° C., preferably less than about 125° C., morepreferably less than about 100° C.). This means that those adductcomplexes are liquid in use. This is particularly advantageous as theexposed surface area of the lanthanide adduct complex during the MOCVDprocess remains substantially constant. This is in direct contrast tothe typically used metal complexes which are of a non-uniformparticulate nature. With those particulate complexes, the smallestparticles will evaporate initially leaving behind the larger particles.Hence, in the known process, the surface area of the exposed metalcomplex decreases and thus the evaporation rate decreases. Furthermore,sintering often occurs with the particles of the present inventionduring the MOCVD process with the result that the surface area:volumeratio, and therefore the evaporation rate, decreases even further. Thelanthanide (β-diketonate)--ligand adduct complexes of the presentinvention permit these problems associated with the known MOCVDprocesses to be overcome or mitigated.

In addition, preferably the neutral (uncharged) donor ligand is anamine, a diamine, a polyamine, a pyridine, a dipyridine, aphenanthroline, an amide, a sulphoxide, an amine-N-oxide, apyridine-N-oxide, a dipyridine-N,N-oxide, a phosphineoxide, an acyclicether, a cyclic ether, a glycol ether, or a polyether, pyridine N-oxidesand 4-alkyl pyridine N-oxides being especially preferred.

Of the other possibilities preferably the diamine is (CH₃)₂ NCH₂ CH₂N(CH₃)₂, the polyamine is (CH₃)₂ NCH₂ CH₂ N(CH₃)CH₂ CH₂ N(CH₃)₂ or(CH₃)₂ NCH₂ CH₂ N(CH₃)CH₂ CH₂ N(CH₃)CH₂ CH₂ NCH₃)₂, the pyridine is C₅H₅ N, the dipyridine is o-(2-C₅ H₄ N)C₅ H₄ N, the phenanthroline is1,10-phenanthroline (4,5-diazaphenanthrene), the amide is (CH₃)₂ NC(O)H,the sulphoxide is CH₃ S(O)CH₃, the amine-N-oxide is (CH₃)₃ NO, and thephosphineoxide is (C₅ H₅)₃ PO or (C₂ H₅)₃ PO.

Preferably the pyridine-N-oxide contains a substituted or unsubstitutedalkyl group.

Preferably the substituent alkyl group is C(CH₃)₃ or C₂ H₅.

Preferably the β-diketonate contains a substituted or unsubstitutedalkyl group and/or a substituted or unsubstituted aryl group.

Preferably the alkyl group is C(CH₃)₃ or n-C₃ F₇.

Preferably the deposition technique is the so-called metal organicchemical vapour deposition (MOCVD).

The organic lanthanide (e.g. yttrium) adducts may be formed by addingLewis base ligand, in liquid or vapour phase, to the lanthanide (e.g.yttrium) -β-diketonate.

The organic lanthanide (e.g. yttrium) adducts may be transported intothe reactor via a liquid-evaporation system.

Thus, the advantages of the adducts of the present invention, especiallythe yttrium adducts, are that they allow the afore-mentioned problemswith the known volatile compounds to be overcome.

In this regard, the present invention is based on the surprising findingthat the problems may be overcome by the combination of certainlanthanide (e.g. yttrium) -β-diketonates and coordinating neutral donorligands according to the present invention.

Without excluding other deposition techniques such as metal-organicspray-pyrolysis (as an example), the method of the invention isparticularly appropriate when applied with MOCVD.

By using volatile and stable compounds according to the invention asstarting material ("precursor"), the MOCVD technique can be used in asimple manner for instance to prepare yttrium-containing materials. Theapplicability of MOCVD for-such materials is of importance especiallyfor preparation of and research on, recently discovered, superconductingmixed metal oxides, buffer layers, anode and electrolyte materials forfuel cells and magnetic oxide materials.

In an alternative embodiment of the process/method according to thepresent invention the organic lanthanide (e.g. yttrium) adducts areformed during the MOCVD process by adding coordinating ligand in liquidor vapour phase to the lanthanide (e.g. yttrium) -β-diketonate(co-evaporation process). Also with this method an increased and moreconstant mass transport of the lanthanide (e.g yttrium) -β-diketonatecan be obtained.

The present invention therefore provides new volatile organic lanthanide(e.g. yttrium) compounds, characterised in that they consist of thecomplex of a lanthanide (e.g. yttrium) -β-diketonate and one or morecoordinating neutral donor ligands according to the present invention.

Suitable neutral donor ligands for the compounds of the presentinvention are:

amines, RR¹ R² N, with R, R¹, R² =H and/or C₁ -C₄ group(s);

di- and polyamines, RR¹ N(CH₂ CH₂ NR²)_(n) CH₂ CH₂ NR³ R⁴, with R, R¹,R², R³, R⁴ =(substituted)alkyl, n=0-5, for instancetetramethylethylenediamine, pentamethyldiethylenetriamine,hexamethyltriethylenetetraamine and the like;

pyridines, C₅ R_(n) H_(5-n) N, with R=C₁ -C₄ group, n=0-5, for instancepyridine and the like;

dipyridines, for instance 2,2'-dipyridine and the like;

phenanthrolines, for instance 1,10-phenanthroline(4,5-diazaphenanthrene) and the like;

amides, RR¹ NC(O)H, with R, R¹ =(substituted)alkyl, for instancedimethylformamide (DMF) and the like;

sulphoxides, RS(O)R¹, with R and R¹ representing a C₁ -C₄ group, forinstance dimethylsulphoxide (DMSO) and the like;

amine-N-oxides, RR¹ R² NO, with R, R¹, R² =H and/or C₁ -C₄ group(s), forinstance trimethylamine-N-oxide and the like;

pyridine-N-oxides, C₅ R_(n) H_(5-n) NO, with R=C₁ -C₄ group, n=0-5, forinstance 4-ethylpyridine-N-oxide, 4-tert-butylpyridine-N-oxide and thelike;

dipyridine-N,N-dioxides, 2,2'-(C₅ R_(n) H_(4-n) NO)₂, with R=C₁ -C₄group, n=0-4;

phosphineoxides, RR¹ R² PO, with R, R¹, R² =H and/or C₁ -C₄ group(s)and/or (substituted)aryl group(s), for instance triethyiphosphineoxide,triphenyliphosphineoxide and the like;

acyclic ethers, ROR¹, with R and R¹ representing a C₁ -C₄ group, forinstance diethylether, dibutylether and the like;

cyclic ethers, (CRR¹)_(n) O and (CRR¹)_(n) O!_(m), with R, R¹ =H and/orC₁ -C₄ group(s), n, m=1-6, for instance tetrahydrofuran, dioxane, crownethers such as 18-crown-6 and the like;

glycol ethers, R¹ -(OCHRCH₂)_(n) OR², with R=H, Me, and R¹, R²=(substituted)alkyl, n=1-6, for instance R=H, R¹ =R² =Me, glyme (n=1,dimethoxyethane, DME), diglyme (n=2), triglyme (n=3), tetraglyme (n=4),hexaglyme (n=6) and the like;

polyethers, RO (CR¹ R²)_(n) O!_(m) H and RO (CR¹ R²)_(n) O!_(m) R³, withR, R³ =(substituted)alkyl and R¹, R² =H, (substituted)alkyl, n=1-4,m=1-6.

The adducts of the present invention, in particular those of theyttrium-β-diketonates according to the invention, possess a much higherstability to hydrolysis than the corresponding lanthanide (e.g. yttrium)-β-diketonates lacking the complexing neutral donor ligand, because dueto the coordination of the neutral donor ligand, there is nocoordination site left for water: the yttrium is coordinately saturated.As a consequence, hydrolysis during handling and the subsequentevaporation in a MOCVD process is prevented.

The synthesis of the lanthanide (e.g. yttrium) -β-diketonate-ligandadducts according to the invention proceeds via a reaction between therequired quantity of ligand and the appropriate lanthanide (e.g.yttrium) -β-diketonate in an inert solvent, such as dichloromethane, orfor example via crystallisation of the appropriate lanthanide (e.g.yttrium) -β-diketonate from the complexing ligand.

The stability of the adducts according to the invention is highest whenthe neutral donor ligand is a pyridine-N-oxide, an amine-N-oxide or aphosphineoxide; preferably the neutral donor ligand is apyridine-N-oxide or an alkyl pyridine-N-oxide.

It has been found that the melting points of the adducts according tothe invention are lowered when the neutral donor ligand contains atleast one (substituted)alkyl group.

Preferably the lanthanide is tri-valent, such as yttrium. The followingstructural formulae therefore give a number of representative examplesof lanthanide adducts according to the present invention:

Ln{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{o-(2-C₅ H₄ N)C₅ H₄ N}. Ln{(CH₃)₃CC(O)CHC(O)C(CH₃)₃ }₃.{1,10-phenanthroline}. Ln{(CH₃)₃CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₂ NCH₂ CH₂ N(CH₃)₂ }. Ln{(CH₃)₃CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₂ NCH₂ CH₂ N(CH₃)CH₂ CH₂ N(CH₃)₂ }.Ln{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₂ N CH₂ CH₂ N(CH₃)!₂ CH₂ CH₂N(CH₃)₂ }. Ln{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃ S(O)CH₃ }. Ln{(CH₃)₃CC(O)CHC(O)C(CH₃)₃ }₃.{C₅ H₅ NO}. Ln{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃}₃.{4-(tert-C₄ H₉)C₅ H₄ NO}. Ln{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{4-(C₂H₅)C₅ H₄ NO}. Ln{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₃ NO}. Ln{(CH₃)₃CC(O)CHC(O)C(CH₃)₃ }₃.{(C₆ H₅)₃ PO}. Ln{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃}₃.{(C₂ H₅)₃ PO}. Ln{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{C₅ H₅ N}. Ln{(CH₃)₃CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₂ NC(O)H}. Ln{CF₃ CF₂ CF₂ C(O)CHC(O)C(CH₃}₃.{(CH₃)₂ NCH₂ CH₂ N(CH₃)CH₂ CH₂ N(CH₃)₂ }.

The general structure formula of the preferred compounds according tothe invention is given on the formula sheet (FIG. 2).

In this structural formula R' and R" represent the side chains of thediketonate, L represents the coordinating neutral donor ligand, and mthe number of coordinating neutral donor ligands. R' and R" may be thesame or different and each is preferably relatively bulky, for exampleCF₃, C₃ F₇ or more preferably tert-C₄ H₉.

As mentioned above, the Y(-β-diketonate)₃ compound Y(TMHD)₃, withoutneutral donor ligand, has a relatively high melting point. With someexamples of adducts according to the invention, which have a much lowermelting point than Y(TMHD)₃ itself, conditions can be realised underwhich, for instance in a MOCVD process, during a longer period of time(several days), a constant mass transport of yttrium compound per unitof time can be maintained.

In a preferred embodiment of the invention, the Y(β-diketonate) compoundis Y(TMHD)₃ and the neutral donor ligand is pyridine-N-oxide, whichcontains at least one of the alkyl groups C₂ H₅ or tert-C₄ H₉.

With compounds according to this preferred embodiment, the most stable,volatile yttrium-β-diketonate-ligand adducts at elevated temperaturesand/or lowered pressures are formed. They also are stable to hydrolysisin air and have low melting points.

The following structural formulae give a number of representativeexamples of yttrium compounds according to the present invention:

1. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(o-(2-C₅ H₄ N}.

2. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{1,10-phenanthroline}.

3. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₂ NCH₂ CH₂ N(CH)₃)₂ }.

4. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₂ NCH₂ CH₂ N(CH₃)CH₂ CH₂ N(CH₃)₂}.

5. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₂ N CH₂ CH₂ N(CH₃)!₂ CH₂ CH₂N(CH₃)₂ }.

6. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{CH₃ S(O)CH₃ }.

7. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{C₅ H₅ NO}.

8. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{4-(tert-C₄ H₉)C₅ H₄ NO}.

9. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{4-(C₂ H₅)C₅ H₄ NO}.

10. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₃ NO}.

11. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(C₅ H₅)₃ PO}.

12. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(C₂ H₅)₃ PO}.

13. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(C₅ H₅ N}.

14. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₂ NC(O)H}.

15. Y{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{(CH₃)₂ NCH₂ CH₂ N(CH₃)CH₂ CH₂N(CH₃)₂ }.

The thermal stability of the compounds 1, 2, 7, 10-12 and 15 accordingto the invention (determined by Simultaneous Thermal Analysis STA!) isshown in Table 1 (discussed later). As the table shows, these compoundsevaporate intact at atmospheric pressure and at temperatures between102° C. and 353° C. The highest amount of residue remaining afterwardsis 2.06% (complex 9), clearly less than with commercially obtainedY(TMHD)₃ (4.40%). The melting peaks, found in the STA spectra, agreewell with the actual melting points, as well as the observedvolatilities.

The volatility and the melting points of the compounds 1-15, as well asthose of the corresponding non-complexed yttrium-β-diketonates, areshown in Table 2 (discussed later). As the table shows, these compoundssublime at lowered pressure (0.01 to 0.05 mm Hg) and at temperaturesbetween 90° C. and 200° C. The compounds 1, 2, 7-12 and 15 are thermallystable under these conditions and evaporate without dissociation. Thismeans that they are especially suitable as a starting material(precursor) for the above mentioned "metal-organic chemical vapourdeposition" (MOCVD) of yttrium containing materials. The compounds 3-6,13 and 14 dissociate into Y(TMHD)₃ and free neutral donor ligand. Thismeans that these compounds are suitabLe as MOCVD precursors in aso-called co-evaporation process, whereby extra neutral donor ligand isadded to the carrier gas.

The low melting complexes 4 and 5 are also suitable in a process inwhich use is made of liquid-evaporation systems.

The vapour pressures as a function of the temperature of the compounds1, 7-9 and 15, as well as those of Y(TMHD)₃, are plotted in FIG. 1 andshown in Table 3. As FIG. 1 and Table 3 show, the order of volatility iscompound 15>>8, 9>Y(TMHD)₃, 7>1. This means that the yttrium compoundsaccording to the invention, despite their much higher molecular mass ascompared with Y(TMHD)₃, have a volatility which lies in the same orderof magnitude and, in the case of compounds 8-9, the volatility is evensomewhat higher. Compound 15 has a volatility which is many times higherthan that of the compounds 1 and 7-9.

The compounds 8 and 9 according to the invention are of specialinterest. These adducts of the non-fluorine-containing complex Y(TMHD)₃have a markedly lower melting point than Y(TMHD)₃ itself. As aconsequence, in the MOCVD process, they may be evaporated from theliquid phase. In addition, they are somewhat more volatile thanY(TMHD)₃. This offers important advantages, especially concerning therealisation of a constant mass transport of the Y-compound in the MOCVDprocess.

The invention also provides a method for the preparation of layeredmaterials which contain yttrium oxide, by means of a depositiontechnique.

Such a method is known, for example, from the publications of Lu andHubert-Pfalzgraf et al., mentioned above.

With the known methods, in particular MOCVD, problems are sometimesencountered with the deposition of yttrium-containing layeredstructures, as a result of the presence of water in, and the resultinghydrolysis of, the starting material (the precursor) from which thedeposition should take place.

The invention can be used to eliminate or mitigate these problems andprovides a method, characterised in that in a deposition technique onestarts with volatile yttrium adducts according to the inventiondescribed above.

Highly preferred embodiments of the present invention therefore includethe following subject-matter or may be defined as follows.

1. Volatile organic yttrium compounds, characterised in that theyconsist of an adduct of an yttrium-β-diketonate and one or morecoordinating neutral donor ligands.

2. A method for the preparation of layered materials which containyttrium oxide, by means of a deposition technique, characterised in thatin the deposition technique one starts with the volatile organic yttriumcompounds according to the present invention.

The following examples illustrate the methods and chemical preparationof typical compounds according to the present invention. All reactionsare carried out in a dry atmosphere and at room temperature unlessstated otherwise.

EXAMPLE 1

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{o-(2-C.sub.5 H.sub.4 N)C.sub.5 H.sub.4 N}.                             (1)

0.64 g (1.0 mmol) of Y(TMHD)₃ and 0.16 g (1.0 mmol) of bipy(2,2'-dipyridine) are dissolved in 15 ml of CH₂ Cl₂. The resultingsolution is stirred for 0.5,h and then evaporated to dryness. Theresidue is sublimed at 160°-170° C./0.06 mm Hg.

Yield: 0.63 g of colourless 1 (80.0%).

Melting point: 185°-188° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.03 (s); δ(CH) 5.45 (s); δ(C₅ H₄) 7.73,7.79, 7.91 and 9.42 (m).

Elemental analysis: found (calculated) (%) C 65.02 (65.00); H 8.31(8.19); N 3.63 (3.53).

STA: melting peak at 188° C.; evaporation from 155°-293° C.; a residueof 0.55% remains afterwards.

EXAMPLE 2

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{1,10-phenanthroline}.                            (2)

Prepared as described for 1 from 0.64 g (1.0 mmol) of Y(TMHD)₃ and 0.20g (1.0 mmol) of phen.H₂ O (1,10-phenanthroline monohydrate). Theresidue, obtained after evaporation of the solvent, is now sublimed at180° C.-200° C./0.03 mm Hg.

Yield: 0.61 g of off-white 2 (75.3%).

Melting point: softening at 235° C. melting at 260°-262° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 0.95 (s); δ(CH) 5.42 (s); δ(phen) 7.65 (m),7.75 (s), 8.23 and 9.72 (m).

Elemental analysis: found (calculated) (%) C 65.71 (66.02); H 7.96(7.95); N 3.55 (3.42).

STA: phase transition peak at 233° C.; melting peak at 269° C.;evaporation from 166°-353° C.; a residue of 1.22% remains afterwards.

EXAMPLE 3

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{(CH.sub.3).sub.2 NCH.sub.2 CH.sub.2 N(CH.sub.3).sub.2 }.                   (3)

Prepared as described for 1 from 0.64 g (1.0 mmol) of Y(TMHD)₃ and 0.12g (1.0 mmol) of Me₂ NCH₂ CH₂ NMe₂. The residue, obtained afterevaporation of the solvent, is not sublimed but dried in vacuo for 2 h.

Yield: 0.67 g of colourless 3 (89.3%).

Melting point: softening at 110°, melting at 145°-150° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.08 (s); δ(CH) 5.67 (s); δ(NMe₂) 2.29 (s);δ(CH₂ N) 2.53 (s).

Elemental analysis: found (calculated) (%) C 61.22 (62.08); H 9.11(9.68); N 3.55 (3.71).

Sublimation: the complex does not sublime as such; at 150° C./0.03 mm Hgrapid dissociation occurs with evaporation of the diamine; the sublimateconsists of Y(TMHD)₃ and a trace of the diamine (¹ H NMR).

EXAMPLE 4

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{(CH.sub.3).sub.2 NCH.sub.2 CH.sub.2 N(CH.sub.3)CH.sub.2 CH.sub.2 N(CH.sub.3).sub.2 }(4)

Prepared as described for 1 from 0.64 g (1.0 nmol) of Y(TMHD)₃ and 0.17g (1.0 mmol) of the triamine. The residue, obtained after evaporation ofthe solvent, is not sublimed but dried in vacuo for 8 h.

Yield: 0.73 g of colourless 4 (90.1%).

Melting point: softening at 55° C., melting at 60°-63° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.10 (s); δ(CH) 5.71 (s); δ(NMe₂) 2.29 (s);δ(NMe) 2.24 (s); δ(CH₂ N) 2.49 and 2.54 (m).

Elemental analysis: found (calculated) (%) C 60.95 (62.15); H 9.84(9.87); N 5.06 (5.18).

Sublimation: the complex does not sublime as such; at 90°-160° C./0.04mm Hg dissociation occurs with evaporation of the ligand; the sublimateconsists of Y(TMHD)₃ and 0.4 eq of the triamine (¹ H NMR).

STA: melting peak at 62° C.; evaporation from 61°-290° C. (differentevaporation rates observed); a residue of 1.3% remains afterwards.

EXAMPLE 5

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{(CH.sub.3).sub.2 N CH.sub.2 CH.sub.2 N(CH.sub.3)!.sub.2 CH.sub.2 CH.sub.2 N(CH.sub.3).sub.2 }.sub.2.                                                  (5)

Prepared as described for 1 from 0.64 g (1.0 mmol) of Y(TMHD)₃ and 0.23g (1.0 mmol) of the tetraamine. The residue, obtained after evaporationof the solvent, is not. sublimed but dried in vacuo for 1 h.

Yield: 0.86 g of off-white 5 (100%); partly solid.

Melting point: 55°-60° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.10 (s); δ(CH) 57.2 (s) δ(NMe₂) 2.29 (s);δ(NMe) 2.26 (s); δ(CH₂ N) 2.46 and 2.54 (m).

Elemental analysis: found (calculated) (%) C 60.57 (62.22); H 10.81(10.02); N 10.18 (6.45); inhomogeneous.

Sublimation: the complex does not sublime as such; at 90°-130° C./0.04mm Hg dissociation occurs with evaporation and condensation of thetetraamine; the sublimate consists of Y(TMHD)₃ and 2.4 eq of thetetraamine (¹ H NMR).

EXAMPLE 6

    Y{(CH.sub.3).sub.2 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{(CH.sub.3 S(O)CH.sub.3 }.                                           (6)

Prepared as described for 1 from 0.64 g (1.0 mmol) of Y(TMHD)₃ and 0.16g (2.0 mmol) of DMSO. The residue, obtained after evaporation of thesolvent, is not sublimed but dried in vacuo for 8 h.

Yield: 0.66 g of colourles6 (93.0%).

Melting point: 156°-158° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.04 (s); δ(CH) 5.63 (s); δ(CH₃) 2.64.

Elemental analysis: found (calculated) (%) C 57.74 (58.66); H 8.71(8.80); N 4.41 (4.48).

Sublimation: the complex does not sublime as such; at 135°-160° C./0.04mm Hg dissociation occurs with evaporation of DMSO; the sublimateconsists of Y(TMHD)₃ and 0.3 eq of DMSO (¹ H NMR).

EXAMPLE 7

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{C.sub.5 H.sub.5 NO}.                                                      (7)

Prepared as described for 1 from 0.64 g (1.0 mmol) of Y(TMHD)₃ and 0.19g (2.0 mmol) of pyNO (pyridine-N-oxide). The residue, obtained afterevaporation of the solvent, is stirred with 100 ml of pentane for 15minutes. The turbid solution is filtered and evaporated to dryness. Theresidue is sublimed at 150°-160° C./0.04 mm Hg.

Yield: 0.56 g of off-white 7 (76.7%).

Melting point: 175°-177° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.05 (s); δ(CH) 5.62 (s); δ(pyNO) 7.32 (t),7.45 (t), 8.55 (d).

Elemental analysis: found (calculated) (%) C 62.02 (62.22); H 8.30(8.46); N 1.89 (1.91).

STA: melting peak at 179° C.; evaporation from 146°-288° C. a residue of0.71% remains afterwards.

EXAMPLE 8

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{4-(tert-C.sub.4 H.sub.9)C.sub.5 H.sub.4 NO}.                              (8)

Prepared as described for 7 from 0.64 g (1.0 mmol) of Y(YMHD)₃ and 0.17g (1.1 mol) of 4-Bu^(t) -pyNO (4-tert-butylpyridine-N-oxide). Theresidue, obtained after evaporation of the pentane solution, is nowsublimed at ±140° C./0.03 mm Hg.

Yield: 0.6 g of colourless 8 (76.1%).

Melting point: 97°-100° C.

¹ H NMR in C₆ D₆ : δ(Bu^(t) TMHD) 1.27 (s); δ(CH) 5.94 (s); δ(Bu^(t)-pyNO) 0.76 (s); δ(pyNO) 6.46 and 8.17 (d).

Elemental analysis: found (calculated) (%) C 64.47 (63.89); H 8.50(8.87); N 1.99 (1.78).

EXAMPLE 9

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{4-(C.sub.2 H.sub.5)C.sub.5 H.sub.4 NO}.                              (9)

Prepared as described for 7 from 0.64 g (1.0 mmol) of Y(TMHD)₃ and 0.13g (1.05 mmol) of 4-Et-pyNO (4-ethylpyridine-N-oxide). The residue,obtained after evaporation of the pentane solution, is now sublimed at140°-150° C./0.03 mm Hg.

Yield: 0.51 g of colourless 9 (67.1%).

Melting point: softening at ±80° C., melting at 93°-98° C.

¹ H NMR in C₆ D₆ : δ(Bu^(t)) 1.28 (s); δ(CH) 5.93 (s); δ(Et) 0.64 (t)and 1.83 (q); δ(pyNO) 6.17 and 8.10 (d).

Elemental analysis: found (calculated) (%) C 63.03 (63.08); H 8.80(8.67); N 1.67 (1.84).

EXAMPLE 10

    Y{(CH .sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{(CH.sub.3).sub.3 NO}.                                                      (10)

Prepared as described for 7 (in a CH₂ Cl₂ /EtOH 1:1 mixture) from 0.64 g(1.0 mmol) of Y(YMHD)₃ and 0.22 g (2.0 mmol) of Me₃ NO.2H₂ O. Theresidue, obtained after evaporation of the pentane solution, is nowsublimed at 180°-200° C./0.05 mm Hg.

Yield: 0.41 g of colourless 10 (57.7%).

Melting point: 199°-202° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.06 (s); δ(CH) 5.58 (s); δ(MeN) 3.33 (s);

Elemental analysis: found (calculated) (%). C 60.48 (60.60); H 9.31(9.26); N 2.24 (1.96).

STA: melting peak at 196° C.; evaporation from 114°-316° C.; a residueof 1.05% remains afterwards.

EXAMPLE 11

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{(C.sub.6 H.sub.5).sub.3 PO}.                                       (11)

Prepared as described for 1 from 0.64 g (1.0 mmol) of Y(TMHD)₃ and 0.28g (1.0 mmol) of Ph₃ PO. The residue, obtained after evaporation of thesolvent, is sublimed at 140°-180° C./0.04 mm Hg.

Yield: 0.84 g of colourless 11 (92.3%).

Melting point: 263°-265° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 0.98 (s); δ(CH) 5.58 (s); δ(Ph) 7.42, 7.52and 7.70 (m).

Elemental analysis: found (calculated) (%) C 66.39 (66.82); H 7.92(7.86); P 3.26 (3.39).

STA: phase transition peaks at 110° and 166° C.; melting peak at 278°C.; evaporation from 186°-343° C.; a residue of 1.01% remainsafterwards.

EXAMPLE 12

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{(C.sub.2 H.sub.5).sub.3 PO}.                                       (12)

Prepared as described for 1 from 0.64 g (1.0 mmol) of Y(TMHD)₃ and 0.134g (1.0 mmol) of Et₃ PO. The residue, obtained after evaporation of thesolvent, is now sublimed at 150°-180° C./0.25 mm Hg.

Yield: 0.63 g of colourless 12 (82.1%).

Melting point: 267°-270° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.01 (s); δ(CH) 5.57 (s); δ(EtP) 1.0-1.2and 1.65-1.77 (m).

Elemental analysis: found (calculated) (%) C 60.66 (60.63); H 9.51(9.33); P 3.88 (4.02).

STA: phase transition peak at 116° C.; melting peak at 273° C.;evaporation from 169°-316° C.; a residue of 0.60% remains afterwards.

EXAMPLE 13

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{C.sub.5 H.sub.5 N}.(13)

0.64 g (1.0 mmol) of Y(TMHD)₃ is crystallised from 3 ml of pyridine. Theproduct is air-dried for 6 h.

Yield: 0.56 g of colourless 13 (78.9%).

Melting point: 129°-131° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.07 (s); δ(CH) 5.70 (s); δ(py) 7.64, 7.75and 8.78 (m).

Elemental analysis: found (calculated) (%) C 63.55 (63.61); H 8.69(8.65); N 2.02 (1.95).

Sublimation: the complex does not sublime as such; at 130°-150° C./0.01mm Hg dissociation occurs with evaporation of the pyridine; thesublimate consists of Y(YMHD)₃ only (¹ H NMR).

EXAMPLE 14

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3. {(CH.sub.3).sub.2 NC(O)H}.                                                  (14)

0.5 g (0.78 mmol) of Y(TMHD)₃ is crystallised from 3 ml of DMF. Theproduct is air-dried for 4 h.

Yield: 0.45 g of colourless 14 (80.8%).

Melting point: 151°-153° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.05 (s); δ(CH) 5.66(s); δ(MeN) 2.88 and2.95 (s); δ(CHO) 8.73 (s).

Elemental analysis: found (calculated) (%) C 60.51 (60.77); H 9.03(9.00); N 2.11 (1.97).

Sublimation: the complex does not sublime as such; at 130°-160° C./0.02mm Hg dissociation occurs with evaporation of the DMF; the sublimateconsists of Y(TMHD)₃ and 0.2 eq of DMF (¹ H NMR).

EXAMPLE 15

    Y{(CF.sub.3 CF.sub.2 CF.sub.2 C(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{(CH.sub.3).sub.2 NCH.sub.2 CH.sub.2 N(CH.sub.3)CH.sub.2 CH.sub.2 N(CH.sub.3).sub.2 }.                                      (15)

Prepared as described from 1 from 1.22 g (1.25 mmol) of Y(FOD)₃ and 0.22g (1.25 nmol) of the triamine. The residue, obtained after evaporationof the solvent, is now sublimed at 120°-150° C./0.05 mm Hg.

Yield: 1.42 g of beige 15 (99.3%).

Meltng point: 85°-88° C.

¹ H NMR in CDCl₃ : δ(Bu^(t)) 1.07 (s); δ(CH) 5.95 (s); δ(NMe₂) 2.29(s,br); δ(NMe) 2.23 (s,br); δ(CH₂ N) 2.54 and 2.72 (m,br).

Elemental analysis: found (calculated) (%) C 40.37 (40.81); H 4.42(4.62); N 3.60 (3.66).

STA: melting peak at 90° C.; evaporation from 102°-273° C.; a residue of0.22% remains afterwards.

EXAMPLE 16

Simultaneous Thermal Analysis (STA) of Y(β-diketonate)₃ -ligandcomplexes.

Simultaneous Thermal Analysis (STA) of various Y(β-diketonate)₃ -ligandadducts is carried out at atmospheric pressure in a nitrogen flow of 40sccm; the heating rate was 20° C./min from room temperature to 600° C.Results are presented in Table 1.

                  TABLE 1                                                         ______________________________________                                                Melting Start       End Evaporation                                                                         Residue                                 Compound                                                                              °C.                                                                            Evaporation °C.                                                                    °C.                                                                              %                                       ______________________________________                                        Y(TMHD).sub.3                                                                         177     129         267       4.40                                    1       188     155         293       0.55                                    2       269     166         353       1.22                                    7       179     146         288       0.71                                    8       104     146         306       1.63                                    9       106     149         297       2.06                                    10      196     114         316       1.05                                    11      278     186         343       1.01                                    12      277     169         316       0.60                                    15      90      102         273       0.22                                    ______________________________________                                    

Table 1 shows selected results of Simultaneous Thermal Analyses of somecompounds according to the invention and of Y(TMHD)₃. The numbers referto the numbers of the structural formulae in the detailed description.

EXAMPLE 17

Sublimation of Y(β-diketonate)₃ -ligand adducts.

Sublimation of various Y(β-diketonate)₃ -ligand adducts is performed atreduced pressure (0.01-0.05 mm Hg) and at temperatures of 90°-200° C.Results are presented in Table 2.

                  TABLE 2                                                         ______________________________________                                        Compound Melting point                                                                            Sublimation point at                                                                        Ligand in                                   (100 mg) °C. 0.01-0.05 mm Hg °C.                                                                  sublimate eq                                ______________________________________                                        Y(TMHD).sub.3                                                                            169-172.5                                                                              130-160       --                                          Y(FOD).sub.3 · H.sub.2 O                                                      108-112    130-160       --                                          1        185-188    160-170       1.0                                         2        260-262    180-200       1.0                                         3        145-150    150           trace                                       4        60-63       90-160       0.4                                         5        55-60       90-130       2.4                                         6        156-158    135-160       0.3                                         7        175-177    150-160       1.0                                         8         97-100    140           1.0                                         9        93-98      140-150       1.0                                         10       199-202    180-200       1.0                                         11       263-265    140-180       1.0                                         12       267-270    150-180       1.0                                         13       129-131    130-150       0.0                                         14       151-153    130-160       0.2                                         15       85-88      120-150       1.0                                         ______________________________________                                    

Table 2 shows volatilities and melting points of some adducts accordingto the invention, as well as those of commercial Y(TMHD)₃ and ofY(FOD)₃.H₂ O. The numbers refer to the numbers of the structuralformulae in the detailed description.

EXAMPLE 18

Vapour pressure measurements on Y(β-diketonate)₃ -ligand adducts.

Vapour pressure measurements on various Y(β-diketonate)₃ -ligand adductsare carried out at temperatures of 90°-180° C. and at a nitrogenbackground pressure of less than 0.01 torr. Volatile impurities, whichmay be present, are removed by pumping several times for 30 seconds atlowered pressure (<0.01 torr), previous to the measurement. Results arepresented in FIG. 1 and Table 3.

                  TABLE 3                                                         ______________________________________                                                  Temperature                                                         Compound  range °C.                                                                        A         B    .increment.H.sub.8 kg/mol                  ______________________________________                                                  140-170   13.919    6.269                                                                              120                                        Y(TMHD).sub.3                                                                           180-200   8.30      3.71 71                                         1         140-180   15.396    6.929                                                                              133                                        7         140-170   13.695    6.172                                                                              118                                        8         120-180   11.687    5.259                                                                              101                                        9         120-180   14.607    6.487                                                                              124                                        15         90-170   5.865     2.466                                                                              47                                         ______________________________________                                    

Table 3 shows temperature dependencies of the vapour pressures of somecompounds according to the invention, as well as those of commercialY(TMHD)₃. The numbers refer to the numbers of the structure formulae inthe detailed description. The vapour pressure data are tabled accordingto the following equation: Log₁₀ P(T)/P₀ !=A-1000 B/T, with P is thepressure in Torr and T is the temperature in degrees Kelvin, P₀ =1. FromB the evaporation enthalpy Δ H₅ (KJ/mol) is calculated.

EXAMPLE 19

MOCVD deposition of Y₂ O₃ from

    Y{(CH.sub.3).sub.3 CC(O)CHC(O)C(CH.sub.3).sub.3 }.sub.3.{4-(tert-C.sub.4 H.sub.9)C.sub.5 H.sub.4 NO}.                              (8)

In a hot-wall MOCVD apparatus, a dry N₂ flow (83 sccm) was led overY{(CH₃)₃ CC(O)CHC(O)C(CH₃)₃ }₃.{4-(tert-C₄ H₉)C₅ H₄ NO} at 160° C., andmixed with N₂ (83 sccm) and O₂ (100 sccm) before entering the reactorchamber. The deposition was performed on a MgO substrate, which isattached to a mass balance by a quartz wire. This balance was protectedby a flow of N₂ (17 sccm). The deposition was performed at a substratetemperature of 850° C. and at a reactor pressure of 2 torr. The growthrate was 3.3 mg/cm² /hr.

EXAMPLE 20 Dy(TMHD)₃.4-tBuPyNO

A dry Schlenk tube was charged under inert atmosphere with Dy(TMHD)₃(2.50 g, 3.51 mmol) and 4-tert-butyl-pyridine-N-oxide (0.53 g, 3.51mmol). Dry toluene (40 cm³) was added to the tube against a strongnitrogen flush. A clear, slightly green solution with faint metalliclustre rapidly formed on stirring. The solution was stirred at ambienttemperature overnight before removing the stirrer bar. Solvent was thenremoved under vacuum until at a minimal level of remaining solvent,crystals formed on the sides of the tube. The solvent was warmed todissolve the solids then gradually cooled to -20° C. to crystallise. Thesolution set as a near-solid mass of crystals (2.678 g) from which onlya small amount of toluene could be removed.

Melting point 109° C. (by STA) C/H/N found versus (calculated) C 59.71(59.42) wt %, H 8.28 (8.12) wt %, and N 1.61 (1.62) wt % STA indicatedthe material to be solvent wet as indicated by a slight weight loss atbelow 100° C. associated with a small exothermic feature. Further weightloss onsets at 187° C. and proceeds in a single, smooth, endothermicstep to a residue of 3 wt % complete by 310° C. This indicates thematerial to sublime intact with accompanying minor amounts ofdecomposition. The material should thus be suitable for use in the MOCVDrig where the volatilisation occurs at lower temperature under reducedpressure. Material was left in the open laboratory overnight and the STAtrace obtained. There was less evidence for the presence of volatilesolvent. The melting point and evaporation range were unchanged, showingthe material to have good stability towards hydrolysis in ambient air.The residue was at 2.8 wt % slightly smaller.

A small sample (0.509 g) of the material was charged to a Schlenk tubefitted with a cold finger and subjected to vacuum sublimation at 0.4mBar, 120° C. rising to 150° C. once the sample had melted. Sublimationrapidly yielded a fine white powder and left a minimal residue. Thepowder (0.39 g recovered, problems with static) was submitted for STA.The trace obtained was identical to those described above, save that alow wet residue, 1.8 wt % remained. This shows the material to sublimeintact at temperatures consistent with use in an LP-MOCVD rig.

A sample of Dy(TMHD)₃ obtained commercially (Lancaster Synthesis) wassubjected to STA under the same conditions as used above. The sampleshowed melting point 180° C. and evaporated to 1 wt % residue over therange 165°-282° C. This shows the adduct complex to be lower melting andonly slightly less volatile.

EXAMPLE 21 Er(TMHD)₃.4-tBuPyNO

A sample of Er(TMHD)₃ (2.53 g, 3.53 mmol) was charged under inertatmosphere to a Schlenk tube-along with 4-tert-butyl-pyridine-N-oxide(0.53 g, 3.53 mmol). Toluene (20 cm³) was, added against rapid nitrogenflush. An orange-pink solution formed after brief stirring. The stirrerbar was removed after about one hour and the solvent removed undervacuum to leave a thick orange oil. The oil was taken up in minimumhexane (10 cm³) and refrigerated. Overnight refrigeration to -20° C.produced a small batch of crystals and some white powder. Furthersolvent was removed under vacuum and the solution once morerefrigerated. A large mass of pink crystals was recovered (1.751 g).

C/H/N analysis, found versus (calculated) for Er(TMHD)₃.4-tBuPyNo, C57.79 (58.11), H 8.32 (8.06) and N 1.61 (1.61) wt %.

STA showed this material to melt at 105° C. before evaporating over therange 172°-300° C. to a low residue (1.8 wt %). Material exposed toambient air overnight gave, within experimental error an identicalresult, demonstrating the good stability towards hydrolysis by ambientair.

The material (0.541 g) was loaded into a Schlenk tube fitted with a coldfinger and subjected to vacuum sublimation at 0.4 mBar, 120°-150° C.About 0.47 g of a glassy pink material was recovered.

The sublimate was subjected to STA under identical conditions to thosedescribed above. There was evidence for some dissociation onsublimation, but the melting point increased only slightly (to 109° C.)and the sublimation range remained the same, with a lower ultimateresidue (1.1%). There is thus good evidence to suggest that thismaterial sublimes intact or near intact.

EXAMPLE 22 Y(HFA)₃.4-tBuPyNO

HFA is 1,1,1,5,5,5-hexafluoroacetylacetonate (or1,1,1,5,5,5-pentane-2,4-dionate).

A dry Schlenk tube was charged under inert atmosphere with Y(HFA)₃(5.165 g, 7.28 mmol) and 4-tert-butyl-pyridine-N-oxide (1.098 g, 7.27mmol). CH₂ Cl₂ (120 cm³) was added against nitrogen flush. The resultingcloudy solution was stirred overnight at ambient temperature under a lowflow of nitrogen. The solvent was removed under vacuum and the resultingwhite powder extracted with refluxing hexane (40 cm³) and separatelywith a similar volume of refluxing toluene. The material was of lowsolubility in both solvents, but white, cubic crystals were obtained oncooling in each case.

The recrystallised samples and the white powder were all subjected toSTA. This showed the materials to be essentially identical, with thatrecrystallised from hexane the purest. The material recrystallised fromhexane had a broad melt at 102° C. An endothermic event associated witha weight loss, corresponding to intact evaporation began at about 200°C. At about 265° C. an exothermic event was observed, completed by 280°C. The weight loss continued smoothly through this event, finishing at300° C., leaving a low 2.7% residue). This shows the material to be agood MOCVD precursor, if not ideal. It is low melting, and stable towell about 200° C. and can be successfully evaporated under typicalMOCVD conditions.

Other modifications of the present invention will be apparent to thoseskilled in the art.

We claim:
 1. In an yttrium-containing material deposition process,wherein the deposition process is a vapour deposition process, theimprovement comprising the use of an yttrium β-diketonate/donor ligandadduct to deposit the material on a substrate and wherein the donorligand is an N-oxide.
 2. The process according to claim 1 wherein thevapour deposition process is a metal-organic chemical vapour deposition(MOCVD) process.
 3. The process according to claim 1 wherein the yttriumβ-diketonate/donor ligand adduct has a melting point of less than about150° C.
 4. The process according to claim 3 wherein the yttriumβ-diketonate/donor ligand adduct has a melting point of less than about125° C.
 5. The process according to claim 4 wherein the yttriumβ-diketonate/donor ligand adduct has a melting point of less than about100° C.
 6. The process according to claim 1 where in the N-oxide is apyridine N-oxide.
 7. In a method of using an yttrium β-diketonate/donorligand adduct in an yttrium containing material deposition process,wherein the deposition process is a vapour deposition process, theimprovement comprising the steps of providing a vapor of said adduct anddepositing the material on a substrate, wherein the donor ligand is anN-oxide.
 8. The method according to claim 7 wherein the yttriumβ-diketonate/donor ligand adduct has a melting point of less than about150° C.
 9. The method according to claim 8 wherein the yttriumβ-diketonate/donor ligand adduct has a melting point of less than about125° C.
 10. The method according to claim 9 wherein the yttriumβ-diketonate/donor ligand adduct has a melting point of less than about100° C.
 11. The method according to claim 7 wherein the N-oxide is apyridine N-oxide.